A confrontation at the Cairo headquarters of a jailed Egyptian opposition leader has left the building gutted by fire.

Seven people were reported injured in Thursday's clash at the liberal Ghad Party building.

Witnesses say a pro-government splinter group of Ghad tried to seize control of the building. It was not immediately clear who started the fire.

Ghad founder Ayman Nour was jailed on charges of fraud in 2005, after he challenged President Hosni Mubarak in the nation's first multi-party presidential election. Nour has denied any wrongdoing and the U.S. has said his imprisonment raises serious concerns about political reform in Egypt.

After Nour's arrest, rivals in the party broke off and chose pro-government politician Moussa Moustafa Moussa as their leader.